Excellent Rectal Temperature Cooling Rates in the Polar Life Pod Consistent With Stationary Tubs

Context: Several tools exist to reduce rectal temperature (T_REC) quickly for patients experiencing exertional heatstroke (EHS). Stationary tubs effectively treat EHS but are bulky and impractical in some situations. More portable cold-water immersion techniques, such as tarp-assisted cooling with oscillation, are gaining popularity because of their benefits (eg, less water needed, portability). The Polar Life Pod (PLP) may be another portable way to reduce T_REC, but few researchers have examined its effectiveness. Objectives: To determine whether the PLP and stationary tub reduced T_REC at acceptable or ideal rates, whether T_REC cooling rates differed by method, and how participants felt before, during, and after cooling. Design: Randomized crossover study. Setting: Laboratory. Patients or Other Participants: Thirteen individuals (8 men, 5 women; age = 21 ± 2 years, mass = 73.99 ± 11.24 kg, height = 176.2 ± 11.1 cm). Intervention(s): Participants exercised in the heat until T_REC was 39.5°C. They immersed themselves in either the PLP (202.7 ± 23.8 L, 3.2 ± 0.6°C) or a stationary tub (567.8 ± 7.6 L, 15.0 ± 0.1°C) until T_REC was 38°C. Thermal sensation and environmental symptom questionnaire (ESQ) responses were recorded before, during, and after exercise and cooling. Main Outcome Measure(s): Rectal temperature cooling rates, thermal sensation, and ESQ responses. Results: Participants had similar exercise durations (PLP = 41.6 ± 6.9 minutes, tub = 42.2 ± 9.3 minutes, t₁₂ = 0.5, P = .31), thermal sensation scores (PLP = 7.0 ± 0.5, tub = 7.0 ± 0.5, P > .05), and ESQ scores (PLP = 25 ± 13, tub = 29 ± 14, P > .05) immediately postexercise each day. Although T_REC cooling rates were excellent in both conditions, the PLP cooled faster than the stationary tub (PLP = 0.28 ± 0.09°C/min, tub = 0.20 ± 0.09°C/min, t₁₂ = 2.5, P = .01). Thermal sensation in the PLP condition was lower than that in the tub condition halfway through cooling (PLP = 1 ± 1, tub = 2 ± 1, P < .05) and postcooling (PLP = 2 ± 1, tub = 3 ± 1, P < .05). The ESQ scores were higher for PLP than for the stationary tub postcooling (PLP = 25 ± 14, tub = 12 ± 9, P < .05). Conclusions: The PLP and the stationary tub cooled individuals with hyperthermia at ideal rates for treating patients with EHS (ie, >0.16°C/min). The PLP may be an effective tool for treating EHS when limited water volumes and portability are concerns. Clinicians should have rewarming tools and strategies (eg, heating blankets) available to improve patients' comfort after PLP use.